6.9.7 Agent Regeneration

The local data structures used by nnagent may become corrupted
due to certain exceptional conditions. When this happens,
nnagent functionality may degrade or even fail. The solution
to this problem is to repair the local data structures by removing all
internal inconsistencies.

For example, if your connection to your server is lost while
downloaded articles into the agent, the local data structures will not
know about articles successfully downloaded prior to the connection
failure. Running gnus-agent-regenerate or
gnus-agent-regenerate-group will update the data structures
such that you don't need to download these articles a second time.

The command gnus-agent-regenerate will perform
gnus-agent-regenerate-group on every agentized group. While
you can run gnus-agent-regenerate in any buffer, it is strongly
recommended that you first close all summary buffers.

The command gnus-agent-regenerate-group uses the local copies
of individual articles to repair the local NOV(header) database. It
then updates the internal data structures that document which articles
are stored locally. An optional argument will mark articles in the
agent as unread.